The DPM Detector. Code:

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1 The DPM Detector P. Felzenszwalb, R. Girshick, D. McAllester, D. Ramanan Object Detection with Discriminatively Trained Part Based Models T-PAMI, 2010 Paper: Code: Sanja Fidler CSC420: Intro to Image Understanding 1/ 53

2 The HOG Detector The HOG detector models an object class as a single rigid template Figure: Single HOG template models people in upright pose. Sanja Fidler CSC420: Intro to Image Understanding 2/ 53

3 But Objects Are Composed of Parts Sanja Fidler CSC420: Intro to Image Understanding 3/ 53

4 Even Rigid Objects Are Composed of Parts Sanja Fidler CSC420: Intro to Image Understanding 4/ 53

5 Figure: Objects are a collection of deformable parts [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 5/ 53 Objects Are Composed of Deformable Parts Revisit the old idea by Fischler & Elschlager 1973 Objects are composed of parts at specific relative locations. Our model should probably also model object parts. Di erent instances of the same object class have parts in slightly di erent locations. Our object model should thus allow slight slack in part position.

6 The DPM Model The DPM model starts by borrowing the idea of the HOG detector. It takes a HOG template for the full object. (If you take something that works, things can only get better, right?) Sanja Fidler CSC420: Intro to Image Understanding 6/ 53

7 The DPM Model DPM now wants to add parts. It wants to add them at locations relative to the location of the root filter. Relative makes sense: if we move, we take our parts with us. Sanja Fidler CSC420: Intro to Image Understanding 7/ 53

8 The DPM Model Add a part at a relative location and scale. Sanja Fidler CSC420: Intro to Image Understanding 8/ 53

9 The DPM Model Each part has an appearance, whichismodeledwithahogtemplate Each part s template is at twice the resolution as the root filter Sanja Fidler CSC420: Intro to Image Understanding 9/ 53

10 The DPM Model Give some slack to the location of the part. Why is this a good idea? Sanja Fidler CSC420: Intro to Image Understanding 10 / 53

11 The DPM Model People are of di erent heights, thus have feet at di erent locations relative to the head. And we want to detect all people, not just the average ones. Sanja Fidler CSC420: Intro to Image Understanding 11 / 53

12 The DPM Model People are of di erent heights, thus have feet at di erent locations relative to the head. And we want to detect all people, not just the average ones. Sanja Fidler CSC420: Intro to Image Understanding 11 / 53

13 The DPM Model People are of di erent heights, thus have feet at di erent locations relative to the head. And we want to detect all people, not just the average ones. Sanja Fidler CSC420: Intro to Image Understanding 12 / 53

14 The DPM Model People are of di erent heights, thus have feet at di erent locations relative to the head. And we want to detect all people, not just the average ones. Sanja Fidler CSC420: Intro to Image Understanding 13 / 53

15 The DPM Model We will, however, trust less detections where parts are not exactly in their expected location. DPM penalizes part shifts with a quadratic function: a(x v x ) 2 + b(x v x )+c(y v y ) 2 + d(y v y ) (here a, b, c, d are weights that are used to penalize di erent terms) Sanja Fidler CSC420: Intro to Image Understanding 14 / 53

16 The DPM Model And finally, DPM has a few parts. Typically 6 (but it s a parameter you can play with). How many weights does a 6-part DPM model have? How shall we score this part-model guy in an image (how to do detection)? Sanja Fidler CSC420: Intro to Image Understanding 15 / 53

17 Remember the HOG Detector The HOG detector computes image pyramid, HOG features, and scores each window with a learned linear classifier [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 16 / 53

18 DPM Detector For DPM the story is quite similar (pyramid, HOG, score window with a learned linear classifier), but now we also need to score the parts. [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 17 / 53

19 Scoring Sanja Fidler CSC420: Intro to Image Understanding 18 / 53

20 Scoring More specifically, we will score a location (window) in the image as follows: nx score(l, p 0 )= max F i HOG(l, p i ) p 1,...,p n i=0 nx i=1 w i def (dx, dy, dx 2, dy 2 ) where F 0 is the (learned) HOG template for root filter F i is the (learned) HOG template for part i HOG(l, p i ) means a HOG feature cropped in window defined by part location p i at level l of the HOG pyramid i w def are (learned) weights for the deformation penalty (dx, dy, dx 2, dy 2 )with(dx, dy) =(x i, y i ) ((x 0, y 0 )+v i )tellushow far the part i is from its expected position (x 0, y 0 )+v i ) Main question: How shall we compute that nasty max p1,...,p n? Sanja Fidler CSC420: Intro to Image Understanding 19 / 53

21 Scoring More specifically, we will score a location (window) in the image as follows: nx score(l, p 0 )= max F i HOG(l, p i ) p 1,...,p n i=0 nx i=1 w i def (dx, dy, dx 2, dy 2 ) where F 0 is the (learned) HOG template for root filter F i is the (learned) HOG template for part i HOG(l, p i ) means a HOG feature cropped in window defined by part location p i at level l of the HOG pyramid i w def are (learned) weights for the deformation penalty (dx, dy, dx 2, dy 2 )with(dx, dy) =(x i, y i ) ((x 0, y 0 )+v i )tellushow far the part i is from its expected position (x 0, y 0 )+v i ) Main question: How shall we compute that nasty max p1,...,p n? Sanja Fidler CSC420: Intro to Image Understanding 19 / 53

22 Scoring Push the max inside (why can we do that?): score(l, p 0 )=F 0 HOG(l, p 0 )+ nx i=1 max F i HOG(l, p i ) w i def def (x i, y i ) p i Sanja Fidler CSC420: Intro to Image Understanding 20 / 53

23 Scoring Push the max inside: score(l, p 0 )=F 0 HOG(l, p 0 )+ nx i=1 max F i HOG(l, p i ) w i def def (x i, y i ) p i We can compute this with dynamic programming. Any idea how? Sanja Fidler CSC420: Intro to Image Understanding 20 / 53

24 Computing the Score with Dynamic Programming Figure: We can compute F i HOG(l, p i )forthefulllevell via cross-correlation of the HOG feature matrix at level l with the template (filter) F i Sanja Fidler CSC420: Intro to Image Understanding 21 / 53

25 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 22 / 53

26 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 23 / 53

27 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 24 / 53

28 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 25 / 53

29 Computing the Score with Dynamic Programming Figure: We can compute these scores e ciently with something called distance transforms (this is exact). But works equally well: Simply limit the scope of where each part could be to a small area, e.g., a few HOG cells up,down,left,right relative to yellow spot (this is approx). Sanja Fidler CSC420: Intro to Image Understanding 26 / 53

30 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 27 / 53

31 Computing the Score with Dynamic Programming Sanja Fidler CSC420: Intro to Image Understanding 28 / 53

32 Detection [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 29 / 53

33 Training You can t train this model as simple as the HOG detector, via SVM. For those taking CSC411: Why not? Sanja Fidler CSC420: Intro to Image Understanding 30 / 53

34 Training You can t train this model as simple as the HOG detector, via SVM. For those taking CSC411: Why not? Because the part positions are not annotated (we don t have ground-truth, and SVM needs ground-truth). We say that the parts are latent. You can train the model with something called latent SVM. For ML bu s: Check the Felzenswalb paper For those with even stronger ML stomach: Yu, Joachims, Learning Structural SVMs with Latent Variables, ICML 09. Sanja Fidler CSC420: Intro to Image Understanding 30 / 53

35 Results Figure: Performance of the HOG detector on person class on PASCAL VOC [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 31 / 53

36 Results Figure: DPM version 1: adds the parts [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 31 / 53

37 Results Figure: DPM version 2: adds another template (called mixture or component). Supposed to detect also people sitting down (e.g., occluded by desk). [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 31 / 53

38 Results Figure: DPM version 3: adds multiple mixtures (components) [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 31 / 53

39 Results [Pic from: R. Girshik] Sanja Fidler CSC420: Intro to Image Understanding 31 / 53

40 Learned Models [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 32 / 53

41 Learned Models [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 33 / 53

42 Learned Models (Takes some imagination to see a cat...) [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 34 / 53

43 Results [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 35 / 53

44 Results [Pic from: Felzenswalb et al., 2010] Sanja Fidler CSC420: Intro to Image Understanding 36 / 53

45 DPM As you already know, the code is available: Trivia: Takes about seconds per image per class. Speed-ups exist. Depending on the size of the dataset, training takes around 12 hours (for most PASCAL classes). Has some cool post-processing tricks: bounding box prediction and context re-scoring. Each typically results in around 2% improvement in AP. In the code, if you switch o the parts, you get the Dalal & Triggs HOG detector. Sanja Fidler CSC420: Intro to Image Understanding 37 / 53

46 Results Sanja Fidler CSC420: Intro to Image Understanding 38 / 53

47 Object Class Detection Pre 2014 HOG detector Deformable Part-based Model Post 2014 (neural networks) R-CNN Fast(er) R-CNN Yolo, SSD [Credit for the slides to follow: Bin Yang] Sanja Fidler CSC420: Intro to Image Understanding 39 / 53

48 The CNN Era [Slide credit: Renjie Liao] Sanja Fidler CSC420: Intro to Image Understanding 40 / 53

49 RCNN: Regions with CNN Features [Slide credit: Ross Girshick] Sanja Fidler CSC420: Intro to Image Understanding 41 / 53

50 Training Sanja Fidler CSC420: Intro to Image Understanding 42 / 53

51 Training Sanja Fidler CSC420: Intro to Image Understanding 42 / 53

52 Training Sanja Fidler CSC420: Intro to Image Understanding 42 / 53

53 RCNN: Performance Sanja Fidler CSC420: Intro to Image Understanding 43 / 53

54 RCNN: Performance Sanja Fidler CSC420: Intro to Image Understanding 44 / 53

55 Faster R-CNN Sanja Fidler CSC420: Intro to Image Understanding 45 / 53

56 Region Proposal Network (RPN) Sanja Fidler CSC420: Intro to Image Understanding 46 / 53

57 Region Proposal Network (RPN) Sanja Fidler CSC420: Intro to Image Understanding 47 / 53

58 Faster R-CNN: Performance Sanja Fidler CSC420: Intro to Image Understanding 48 / 53

59 Car Example [Slide credit: Joseph Chet Redmon] Sanja Fidler CSC420: Intro to Image Understanding 49 / 53

60 Car Example [Slide credit: Joseph Chet Redmon] Sanja Fidler CSC420: Intro to Image Understanding 49 / 53

61 Car Example [Slide credit: Joseph Chet Redmon] Sanja Fidler CSC420: Intro to Image Understanding 49 / 53

62 Real Time Object Detection? Sanja Fidler CSC420: Intro to Image Understanding 50 / 53

63 YOLO: You Only Look Once [Slide credit: Redmon J et al. You only look once: Unified, real-time object detection. CVPR 16] Sanja Fidler CSC420: Intro to Image Understanding 51 / 53

64 YOLO: Output Parametrization [Slide credit: Redmon J et al. You only look once: Unified, real-time object detection. CVPR 16] Sanja Fidler CSC420: Intro to Image Understanding 52 / 53

65 SSD: Single Shot MultiBox Detector [Slide credit: Wei L, et al. SSD: Single Shot MultiBox Detector. ECCV 16] Sanja Fidler CSC420: Intro to Image Understanding 53 / 53

66 That s It For CSC But There Is Much More of Computer Vision For Those Interested! Sanja Fidler CSC420: Intro to Image Understanding 54 / 53